Height Blend Mask and Vertex color based Material Blending Shader
To add the height map on your blending gradient (I use vertex colour, but you can also take a UV channel or just use a image texture), you just need to run it through a Smoothstep node like so:





The vertex colour is the gradient, I run it through a smooth step node. Edge 0 is the height map, edge 1 controls how harsh/soft the blending is. Use the result as the factor to blend your shaders or textures!

This is loosely based of of the documentation for Unity Shaderforge an old unity plugin: http://acegikmo.com/shaderforge/wiki/index.php?title=Advanced_Texture_Splatting